Just open up whm and learn the job, if you're good enough to do all this content on CNJ, you'll be amazing on whm with the extra tools and the higher DPS items. You'll have higher mind stats for bigger cures, higher int when you cleric stance and trust me, whm is a heck more fun with Holy.

You'll be great at it. Staying CNJ just to make a point that the game is lulzy is kinda di--ckish. Dungeons are not supposed to be hard, they cater to the casual population and are meant to be completed with the barest minimum. You're just bringing grief to yourself. Japanese players run blacklisting forums where they report to each other players they need to be weary of and you'll end up on one of them before too long. You will be basically barred from doing endgame stuff on your server and it would be an awful experience (if you're even interested in doing that stuff, but that's the challenge you're looking for, I believe).